New Bouguer Gravity Maps of Venezuela: Representation and Analysis of Free-Air and Bouguer Anomalies with Emphasis on Spectral Analyses and Elastic Thickness

Javier Sanchez-Rojas

doi:10.1155/2012/731545

Abstract

A new gravity data compilation for Venezuela was processed and homogenized. Gravity was measured in reference to the International Gravity Standardization Net 1971, and the complete Bouguer anomaly was calculated by using the Geodetic Reference System 1980 and 2.67 Mg/m3. A regional gravity map was computed by removing wavelengths higher than 200 km from the Bouguer anomaly. After the anomaly separation, regional and residual Bouguer gravity fields were then critically discussed in term of the regional tectonic features. Results were compared with the previous geological and tectonic information obtained from former studies. Gravity and topography data in the spectral domain were used to examine the elastic thickness and depths of the structures of the causative measured anomaly. According to the power spectrum analysis results of the gravity data, the averaged Moho depths for the massif, plains, and mountainous areas in Venezuela are 42, 35, and 40 km, respectively. The averaged admittance function computed from the topography and Free-Air anomaly profiles across Mérida Andes showed a good fit for a regional compensation model with an effective elastic thickness of 15 km.

Highlights

A new gravity data compilation for Venezuela was processed and homogenized
This study has four main aims: (1) to study the correlation between the Bouguer anomalies and the known regional geology by means of regional and residual gravity anomaly separation; (2) to estimate the continental crust thickness (Moho) using a spectral technique and to correlate it with Moho estimations derived from independent geophysical techniques (i.e., P-wave velocity models, which stem from wide-angle refraction seismic and the results from receiver function methods); (3) to use the coherence-admittance
A new Bouguer gravity map of Venezuela was developed based on an up-to-date dataset available in the country

Summary

Introduction

A new gravity data compilation for Venezuela was processed and homogenized. Gravity was measured in reference to the International Gravity Standardization Net 1971, and the complete Bouguer anomaly was calculated by using the Geodetic Reference System 1980 and 2.67 Mg/m3. It is commonly accepted that extensive volcanism in the mid to late Cretaceous (∼90–110 Ma) resulted in the formation of the Caribbean Large Igneous Province and a thickening of large areas of the Caribbean crust Around this time, the Caribbean plate (CA) initiated an eastward migration relative to South America (SA) [6,7,8,9,10]. The Barinas-Apure and Eastern Venezuelan sedimentary basins are separated by a geomorphologic-structural high called El Baul High, formed by an igneous-metamorphic complex. This massif was described by Bellizzia [15], who differentiated several granitic, volcanic, and metasedimentary units and subunits. According to Schubert [20] and Kohn et al, [21] this convergence has the main period of shortening during the Oligocene-Miocene, and evidence suggest that there is still significant present-day deformation

Objectives

Results

Conclusion